Research Report No. 11, Pile Supported Structures in … the head of the piles down to elevations of 20 to ... hydraulic jack in 5-ton increments. ... quired to drive each pile was

FiguTB 2.-Excavation and foundation construction, Willard Pumping Plant No. I.

TABLE 1.-Soil properties

Property No. oftests

Maximum Minimum Average

15

15

15

18

18

22

22

3

52

29

1

100

54

17

21

3

3316

4123

.5 .967

25

2

3

2

84:

37

7

8

3

8345

2229

o0

3II

10

35

74

4 62

Liquid limit. ; Plasticity index, Ip. ,

Liquidityindex,IL ,.., , ,

Unit weight, 'YJ in pounds per cubicfoot. Watercontent, in percentage. ;,.

Compressive strength, qu' inpsi... , ;Axial ..I

straln,Ea, atqu,mpercentage " Triaxialcohesion,inpsi... , Standard penetration resistance, in blows per foot :

30-60feet ,...

60-loofeet Maximum vane shear stress, in psi :

Natural , Remolded

327/T.-632 o--es-2

Figure 19.-Installation of 5-foot-diameter casings.

Figure 20.-Driving test pile 4.

across the top of the casing. The breaker ball andbeam may be seen at left center in figure 19.

Equipment and Procedures

Driving piles-- The contractor's pile-driving rig con-sisted of a crane with a 55-foot boom and extended

hanging leads 70 feet long ( figure 20) .The pilingswere driven with a single-acting air hammer ( figure

21) , equipped with a standard base.The piles were equipped with steel driving shoes,

and the head of each pile was fitted with a steel bandto prevent damage during driving.

The contractor elected to use a follower extension todrive the head of the piles down to elevations of 20 to25 feet below the existing ground elevation. The ex-tension shown in figure 22 was fabricated from a 22-foot length of 12-inch-wide flange beam, 65 poundsper foot. The same extension or a similar one was usedto apply the bearing and pull loads to the test piling.

The bracing shown in figure 23 was used to guidethe piles at the start of the drive. When the heads ofthe piles were close to the ground surface, the exten-sion was added, and driving was continued to the spe-cified driving resistance.

The design driving resistance of 40,000 pounds was

Fi,ure 21.-Pile driving hammer.

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computed by the formula given in the specifications tobe 24 blows per foot with the Vulcan No.1 hammer.Excessive driving resistance of 80,000 poUJ\ds wascomputed to be 60 blows per foot by the same formula.The specified formula is as follows :

beam and welded to the 5-foot-diameter steel casingsfor the tests on piles 1 through 4 ( figure 25) .The re-action load for piles 3 through 6 was supplied by twotractors with dozer blades, as shown in figure 26.

The bearing tests were performed according toASTM Test Designation Dl 143-57T, "TentativeMethod of Test for Load-Settlement Relationship forIndividual Piles under Vertical Axial Loads". The testloads were applied to the piles with a 100-ton-capacityhydraulic jack in 5-ton increments. All settlement read-ings were made on a 5~-inch by 5~-inch by Y4-inchsteel plate, which was attached to the top end ofa 3/4-inch pipe. This pipe extended from the groundsurface down to a lag screw in the pile head. The tipof the dial indicator gage ( 4-inch travel, O.OOl-inchgraduations) rested on the steel plate. An engineer'sscale was also attached to this plate and was read witha transit which was referenced to a level rod and target,as shown in figure 26. Both the level rod and the tripodlegs of the transit were buried in the ground about 18inches. A typical installation of the dial gage and engi-neer's scale is shown in figure 25. The gage in thebackground measured the movement of the pile headwhile the tip of the gage rested on the top of the3/4-inch pipe. The gage in the foreground is resting on abracket attached to the hydraulic jack, which moved

P-==~

8+0.1

where:p= bearing resistance in pounds, 40,000 or

80,000;W =weight in pounds of striking part of hammer,

5,000;H = stroke or fall in feet, 3 ;E= efficiency, 80 percent;S=average penetration in inches per blow for

at least 10 to 20 blows.

A continuous record of the number of blows re-quired to drive each pile was obtained and is shown infigures 14,15, and 16.

Bearing tests-Heavy construction equipment wasused as the reaction load for all the vertical bearingtests. Two tractors w~th dozer blades and a crane sup-plied the necessary weight for the 100-ton tests onpiles 1 and 2 ( figure 24) .As an added precaution, 1 Y4-inch reinforcing bars were placed over the reaction

Figure 22.-Pile driving extension.

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Figure 23.-Guide bracing for test piles.

with the extension such that this second gage meas-ured the vertical movement of the upper end of theextension. This measurement was taken on the firstfew tests, then discontinued, as it included the takeupof slack in the extension.

The dial gages were supported by a reference beamwhich was independent of the reaction load and thetest pile. The reference beam for the tests on piles 4,5,and 6 was an 18-foot length of 4-inch channel, 7.7pounds per foot, welded to two steel stakes driveninto the ground about 2V2 feet. During the testing ofpile 4, the entire area within about 10 feet of the casingsettled and caused the reference beam to settle also.To correct this, a 3-inch channel, 5.7 pounds pt::r foot,and the 4-inch channel were spliced to form a 34-footbeam. The bearing area of the stakes, to which thebeam was attached, was increased by welding 8- by8-inch steel plates to the lower end of the stakes. This34-foot reference beam was used for the tests on piles1, 2, and 3 (figures 25 and 26) .

Another instrument which was used on the bearingtests of piles 5 and 6 is the pencil device for recordinglateral movement of the pile extension shown in figure27. The device was useful to detect lateral movementof the reaction beam when the limit of the reactionload was reached and the load shifted slightly. The useof this device was discontinued when the contractor

started attaching the reaction beam to the casing with1 Y4-inch reinforcing bars.

Pull tests--Figure 28 illustrates the general test setup for the pull tests except that, for the tests on pile1, two 18-inch I-beams, 54.7 pounds per foot, placedside by side were used.

The pull tests were performed according to the pro-cedure given in the specifications. All loading incre-ments and unloading decrements for the 20-ton pulltest on pile 1 were double those specified for the 10-tonpull tests. The 30-ton failure pull test on pile 1 wasapplied in 5-ton increments at 5-minute time intervals.The gage and level readings were made in a manneridentical to those ,taken for the bearing tests.

The pull force was transmitted to the pile by a 12~inch-wide steel band. The band was formed by twosemicircular pieces bolted together with 1 Y4-inch boltsand recessed into the butt of the pile. These were alsospiked to the pile with six mine rail spikes. The pullingbars shown in figure 28 were attached to the follower,which in turn was attached to the band on the pile bya similar set of pulling bars.

Vane shear tests-To investigate the possible effectof remolding caused by pile driving, vane tests wereperformed at Plant No.1 in the vicinity of piles 1 and2. These tests were made at depths of 45 and 60 feetbefore driving piles, and again within 24 hours after

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Figure 25.-Test set-up on pile 3.

piles were driven. All the tests were conducted accord-ing to Designation E-20, "In-place Vane Shear Test",First Edition of the Bureau of Reclamation EarthManual.. with one exception. The remolded portion ofthe test was repeated several times with the vane beingrotated 360° between each repetition.

driving piles 1 and 2. The after-driving vane tests were

made within 3 feet of each pile and at the same depths.

After the testing of piles 1 and 2 was complete, a third

series of vane tests was made within 1 ~ feet of piles 1

and 2 and at the same depths as previous vane tests.

These tests were performed about 6 weeks after the

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FiRure 26.-Loading for piles 3 through 6.

Figure 27.-Lateral movement measuring device.

27

Figure 28.-Pull test equipment on pile 5.

ever, these piles encountered occasional layers of densesand. The driving records of piles 3 and 4 were similar,and the minimum trends of the curves indicate bearingcapacity at 90-foot depth, by the EN formula, of from16 to 30 tons, and a 40-ton value of bearing capacitywas reached for the long pile (pile 3) when it ap-proached, or just entered, the deeper firm layer. Thedriving record of piles 1 and 2, shown in figure 15, in-dicates slightly lower minimum driving resistancetrends than that shown by piles 3 and 4. The penetra-tion resistance test values," shown in figure 15, were alsoless for this location than those'shown in figure 14.' With the exception of the high-driving resistance

which developed for a short distance after each delayin driving, excessive driving resistance was developedonly on pile 3, as shown on figure 14. This was withinthe range where jetting could be wed at the directionof the contracting officer. Since the pile tip was verynear the desired depth, it was decided to stop driving at102.1 feet and not use jetting. Pile 3 drove as if the tipwas already in the silt and fine sand stratum, whichthe log indicated was at 105 feet. Since pile 3 was theonly one which developed excessive driving resistance,no jetting was used for any of the piles.

T est Results

Pile driving-At each of the three drill hole loca-tions selected for tests, two piles were driven, a longpile and a pile driven to a tip location in the upperstrata of material showing relatively high values by thepenetration resistance test. The depths of drive speci-fied were to be within certain limits. The driving rec-ords given in figures 14 through 16 show the depths towhich the piles were driven.

Pile 6 at Plant No.2 (figure 16) \vas driven to nearlythe limiting depth but also reached a bearing capacityof 20 tons by the EN formula. Some difficulty was en-countered during the driving of pile 6 because this wasthe first pile driyen and because it was a pile with arelatively large tip of more than 8 inches in diameter.This may partly contribute to a relatively high bearingcapacity. The longer pile, No.5, at this location, onlyreached a bearing capacity of about 11 tons by the ENformula at the same depth as pile 6, but when drivento a depth of 95 feet into the lower, relatively firm claystratum, a value of 28 tons by the EN formula wasobtained.

Piles at Plant No.1 were likewise driven to twodifferent depths, as shown in figurp,5 14 and 15. How-

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